Septic Vulnerability

It’s time to face the inconvenient truth of sea level rise in South Florida.

Though coastal areas are vulnerable to this all too real threat, inland areas are similarly facing the reality of sea level rise. The problem is septic tanks, something Miami-Dade County has by the tens of thousands (108,000 to be exact).

A new report by Miami-Dade County details the septic vulnerability that threatens practically every corner of the city. With every bit of sea level rise South Florida experiences, the groundwater also rises. The more groundwater rises, the more our septic systems are prone to failure. This is because the process that allows septic tanks to function properly becomes compromised the high the groundwater is.

This graphic illustrates the relationship between sea level and groundwater level.

Rising sea level means rising groundwater.

In a functioning septic system, a liquid waste in the septic tank empties into the drainfield. From the drainfield, that liquid waste filters down through a layer of dry soil. The key there is dry soil. According to the Florida Department of Health, the minimum amount of space between the bottom of the drainfield and the water table is 24 inches during the rainy season. When the groundwater rises, that space of dry soil between drainfield and water tables shrinks, the soil goes from dry to soggy. Liquid waste doesn’t filter through soggy soil properly. When the soil is permanently soggy, the wastewater flows through it quicker which cuts down on filtering time, allowing the wastewater to enter the groundwater and aquifer without being properly filtered. This means contaminated water, rather than completely treated wastewater, enters the aquifer and contaminating drinking water.

These two figures offer a visual of how rising groundwater can compromise existing septic tanks

This poses a huge environmental and public health risk. The septic systems across Miami-Dade County are consistently recharging the Biscayne Aquifer. Failing septic systems risk contaminating this freshwater aquifer that provides drinking water to the County. This contamination can lead to the outbreak of water borne diseases, causing a widespread public health risk. Additional environmental risks include contamination of coastal waters.

With over 100,000 properties using septic tanks, Miami-Dade County has a significant threat on its hands. The report estimated that by 2040 more 64% of those properties, over 67,234 properties, could be periodically failing due to rising sea levels and groundwater. It’s important to remember that coastal homes aren’t the only ones at risk when it comes to septic tanks. In Coral Gables there are 2,930 septic tanks, 260 of which will have periodic problems by 2040 due to sea level rise. Of the 5,088 homes with septic tanks in Pinecrest, 1,808 will also have periodic problems by 2040. The list goes on and on: Sweetwater, Hialeah, Miami Gardens, Doral.

This map shows the areas in Miami-Dade County with vulnerable septic systems.

The solution to this problem is extending sewage lines and transition septic systems to sewage lines. But connecting over 100,000 properties to the sewer system is about as expensive as it sounds. Specifically, the estimated price could be as high as $3.3 billion. That $3.3 billion only covers residential properties, though the

As the report states, “Septic systems were not designed with the assumption that groundwater levels would rise gradually over time.” Not accounting for future gradual changes has already caused 58,000 residential septic systems to be “periodically compromised” by wet seasons and storm conditions that can cause rising groundwater.

Sea level rise is happening and the time has come to stop burying our heads in the sand. Every minute spent trying to refute the facts is a minute wasted; a minute not spent trying to find solutions to the problems sea level rise poses to our community. Our leaders need to think not just of their own terms but of the future of the city.

To learn more about septic tanks, read our blog post, Septic Skeptic, to learn more about septic systems. The full report cited in this blog post can be found here.

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